This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 11-343204, filed Dec. 2, 1999, the entire contents of which are incorporated herein by reference.
The present invention relates to a portable electrical equipment such as a portable telephone or a personal computer, and in particular, to an imaging system mounted in a camera module equipped in such a portable electrical equipment.
In recent years, a camera module for picking up an image has been mounted to a portable information device such as a portable telephone or a notebook type personal computer. Also, a downsizing of the portable information device itself is kept on. According to this trend, requirement for the downsizing of a camera module is raised. Meanwhile, an image sensor using a CCD (Charge Coupled Device), a CMOS or the like achieves a small area of 3.6xc3x972.7 mm (diagonal length: 4.5 mm) in spite of a high quality such as a VGA format (640xc3x97480 pixels). In addition, when this image sensor is mounted on a printed circuit board together with a driving circuit and a cover glass, the thickness thereof is about 2.5 mm. When an image sensor having a pixel density of such a VGA format or more, of course, an image pick-up optical system having a high resolution which can exploit the pixel density thereof is required.
Such an optical system comprises a plurality of lenses in a conventional art. For example, when an image sensor with an image size of 3.6xc3x972.7 mm in a VGA format is used, an optical system as shown in FIG. 1 can be obtained. In an imaging system 20 configured by two lenses, the aperture ratio is F/2.8, the focal length is 3.45 mm, an optical system length L from a front surface of a lens to an imaging surface is 5.93 mm. A horizontal total angle of view and a diagonal total angle of view which include a distortion are 56xc2x0 and 67xc2x0, respectively, as a visual field thereof. In a case that this imaging system is used for the camera module, the thickness from a lens-barrel to a backside of the sensor becomes about 8.9 mm (=5.93+2.5+0.5 (corresponding to a projection size of the lens-barrel)).
Now, assuming that the above-mentioned optical system is mounted on, for example, a portable telephone having the thickness of 10.5 mm and configured by a case with the thickness of about 0.9 mm, the thickness of the space surrounded by the case becomes about 8.7 mm. Therefore, a module having the thickness of about 8.9 mm in the optical direction can not be mounted on such a portable telephone. For this reason, a thickness in an axial direction is required to be 8.5 mm or less in a camera module, which is mounted on such a small portable terminal device. Accordingly, the size of the imaging system depends on the structure of a printed circuit board or the like, but the size of the imaging system including the length of the projection portion of the lens-barrel protecting the imaging system must be about 6.0 mm or less.
By shortening a length of an imaging system such as 6.0 mm or less, the diameter of the lens shortens, and it is difficult to form the lens surface with a diameter of 1 cm or less in a highly accurate aspheric shape. Therefore, a lens surface shape with an excellent formability is required in mass production.
An object of the present invention to provide a lens, a camera module, a lens device and an electrical equipment comprising any one of them, which are applicable to the above case.
A lens according to the present invention comprises a lens, which is a single and meniscus lens whose optical surface is aspheric surface, and when a refractive index of the lens is represented by n, a central thickness thereof is represented by t, a radius of curvature of a concave face thereof is represented by r1, the radius of curvature of the convex face thereof is represented by r2, and a focal length thereof is represented by f, the lens satisfies the following equations:                     -        0.2             less than                         (                                    n              -              1                        r1                    )                /        f             less than       0        ,          
        ⁢          0.08       less than                         (                                    1              -              n                        r2                    )                /        f             less than       0.1        ,          xe2x80x83        ⁢    and        0.35     less than           t      /      f         less than           0.55      .      
A camera module according to the present invention comprises a lens as mentioned above, and an aperture iris provided on a side of an incident surface of the lens to restrict the amount of an incident light on the lens, a lens-barrel holding a aperture iris and the lens, an image sensor fixed to a hollow portion of the lens-barrel opposed to the lens.
A lens device according to the present invention comprises a lens, and an aperture iris provided on an incident surface side of the lens to restrict an amount of a incident light on the lens, the lens comprises a lens, which is a single and meniscus lens whose optical surface is aspheric surface, and when a refractive index of the lens is represented by n, a central thickness thereof is represented by t, a radius of curvature of a concave face thereof is represented by r1, the radius of curvature of the convex face thereof is represented by r2, and a focal length thereof is represented by f, the lens satisfies the following equations:                     -        0.2             less than                         (                                    n              -              1                        r1                    )                /        f             less than       0        ,          
        ⁢          0.08       less than                         (                                    1              -              n                        r2                    )                /        f             less than       0.1        ,          xe2x80x83        ⁢    and              0.35       less than               t        /        f             less than       0.55        ,          xe2x80x83        ⁢    and  
when a distance between a concave face of the lens and the aperture iris is d1, the lens device satisfies the following equation:
0 less than d1/f less than 0.1
An electrical equipment, which is portable and performs a predetermined operation, comprises a lens device or a camera module as mentioned above mounted on a circuit board provided on the electrical equipment.
In the above-mentioned lens or lens device, a diameter of a concave surface or a convex surface of the lens is equal to or less than 1 cm.
In the above-mentioned camera module, a total length from the aperture iris to the image sensor is equal to or less than 6 mm.
As mentioned above, according to the present invention, an optical system with small size and capable of imaging with high resolution can be provided with one aspheric lens to be able to contribute an improvement in portability of an electrical equipment, which processes image information.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.